Telephone-exchange system.



Patented November 29, 1904.

ATENT FFICE.

EDWIN H. SMYTHE, OF FREEPORT, ILLINOIS, ASSIGNOR TO \VESTERN ELECTRICCOMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 776,435, dated November29, 1904. Application filed May 24, 1902. Serial No. 108,778. (Nomodel.)

To (tZZ whom it may concern:

Be it known that I, EDWIN H. SMYTHE, a citizen of the United States,residing at Freeport, in the county of Stephenson and State of Illinois,have invented a certain new and useful Improvement in Telephone-ExchangeSystems, of which the following is a full, clear, concise, and exactdescription.

My invention relates to telephone-exchange systems, and moreparticularly to apparatus for use at multiple switchboards, its objectbeing to permit an operator who has a call for a line which is alreadybusy at some other section of the board to take the necessary stepspreliminary to completing connection, such as the insertion of the plugin a springjack of the line, after which a complete operative connectionwith the line will be automatically made as soon as the connection atthe other section has been removed and the line is again freethat is tosay, the operator by inserting the plug in the spring-jack of a busyline brings the calling-line into such relation to the called line thata complete operative'connection will be automatically established at theinstant the called line ceases to be busy. Heretofore it has been usualfor the operator before making connection with a line called for to testthe line and if it is found free to complete the connection; but if theline wanted is found to be already connected at some other section thecalling party is simply notified that the line is busy and that he mustmake a second call. lVhen the calling party makes his second call, itmay be that the line wanted has been free and again connected to someother line, so that further delay and annoyance results. In accordancewith my invention the calling party is brought instantly andautomatically into operative connection with the line wanted as soon asthe connection which may already exist at some other section has beenremoved. My invention further contemplates signals for the calling-lineto indicate automatically the busy condition of the called line and alsoto indicate the instant it is free.

My invention will be especially valuable where the calling-line is atrunk-line to permit the incoming-trunk operator who has a call comingin over one of the trunk-lines to give that call precedence overordinary calls from local lines and to take all the preliminary stepsfor the establishment of the trunk connection, so that the connectionwith the calling-line may be operatively completed the instant thecalled line becomes free.

In the accompanying drawing, which illustratcs the preferred embodimentof my invention, I have shown a trunk-line extending from anansweringswitehboard A to a trunkboard B. A telephone-line is shownextending from a toll-station A to a spring-jack (t at the board A, andanother telephone-line is shown extending from a substation B tomultiple spring-jacks at the board B. The line to station A is of a typein which'a local battery is employed at the substation for exciting thesubscribers transmitter, and a handgenerator is employed. for operatingthe callannunciator at the answering-switchboard. The apparatus of theline to station B is of another well-known type, in which automaticsignals are employed and the substation-transmitter is excited bycurrent from a central battery brought into circuit therewith by way ofthe plug with which connection is made with the line at theexchange-switchboard. Multiple spring jacks or connection terminals 7) 5are provided for the line to station B at the switchboard B, each ofsaid spring-jacks having the usual short and long line springs, whichare connected, respectively, with the conductors 1 2 of the line, andeach spring-jack having also the usual thimble or test-ring 6 Thethimbles of all the jacks of the line are connected together by aconductor 3, which extends to earth through the winding of the usualcutoff relay 0 of the line. two of these multiple spring-jacks, of whichthere may actually be a large number, one at each section of themultiple switchboard, so that connection may be made with the line atany section by inserting a plug in the springjack at that section. Inassociation with the lower one of the two spring-jacks shown in thedrawing I have illustrated a portion of an I have shown only.

operators plug-circuit of a well-known and standard type. The plug hasthe usual tip, ring, and sleeve contacts, adapted to engage,respectively, with the short and long line springs and the test-ring Zof the jack into which such plug is inserted, and the third contact ofthe plug is connected, as usual, through a supervisory signal with thefree pole of a grounded battery (Z, which is bridged between the twomain conductors, leading to the tip and sleeve of the plug. The operatorat each section of the multiple switchboard (except where the incomingtrunks are located) is provided with a number of plug-circuits foruniting lines. Vhenever a connection is made at any one of the multiplespring-jacks of a line, the electrical condition of allthe multiplespring-jacks is changed by the connection of the grounded battery (Z byway of the third contact of the plug and the test-ring of the jack intowhich it may be inserted to the test-conductor 3, and so to thetest-rings of all the jacks-that is to say, the insertion of a plug intoany one of the multiple jacks establishes a test-potential at thetest-rings of all the other multiple jacks. The existence of thispotential may be detected at any section of the board by touching agrounded conductor containing a testing instrument to the thimble of thejack at that board. This busy-test system well known in the art, itbeing the usual practice for the operator before inserting a plugintothe spring-jack of a line called for to touch the tip of her plug, whichis connected to earth through a winding of her telephone induction-coil,to the thimble of the jack. If a potential exists at the test-ring ofthe jack as a result of connection with the line at some other sectionof the board, a click will be produced in the operators telephone, whichnotifies her that the line is busy.

In association with the upper one of the spring-jacks Z21 have shown anincoming-trunk plug 6, which forms the terminal of a trunkline extendingin two limbs L 5 from the tip and ring contacts 0 6 respectively, of thetrunk-plug to the line-springsff of a spring jack f at the distantanswering-board A. The plug 6 has a third contact or sleeve 6 whichregisters with the test-ring Z of any jack into which the plug may beinserted, and this sleeve-contact forms one terminal of a conductor 6,the other end of which is connected to the armature switch-lever g of anelectromagnetic switch g. The switch-lever g is normally maintainedclosed againsta back contact which is connected to earth through thehigh-resistance test-magnet h. \V hen the electromagnetic switch 5 isexcited, it draws the armature g away from its back contact, thuscutting off the test-magnet Zt, and connects said lever instead to afront contact, which is connected through a resistance with the freepole of the grounded battery (Z. While four batteries (marked (Z) areshown at the switch- 1 board B, it is understood that in accordance withthe usual practice a single central battery may be employed, which maybe connected as indicated. When the lever g is in its normal position,the test-magnet Z1 is thus connected in a grounded branch from thesleeve 6 of the trunk-plug, and when the plug is inserted in aspring-jack this magnet is sensitive to the electrical condition of thetestring of such jack. If a connection already exists at some other jackof the line, so that there is a potential at the test-ring, the magnetIL will be excited; but if no connection exists there will be nopotential on the test-ring and the magnet It will be inert.

The magnet it has an armature which is connected to earth, and the backcontact, against which said armature normally rests, forms the terminalof a conductor 7, leading through the winding of magnet g to thearmature ZJ of a magnet Z3. A conductor 8 extends from the free pole ofbattery (Z, through the contacts of a plug-seat switch Z, to oneterminal of the winding of magnet k and from the other terminal thereof,through a switchspring 75 and its resting contact-anvil, to a connectionwith the conductor 6 between the sleeve of the plug and the switch-leverg. W'hen the magnet Z0 is excited, it draws its armature It against thecontact-spring Z2 and after this contact is made spring k is separatedfrom its resting contact-anvil, thus cutting off the connection ofconductor 8 with conductor 6. The magnet Z; has another armature, kwhich controls the tip-strand i of the trunk-line. The armature Z5 isconnected to the tip of the plug and normally breaks the conductor 4: atits front contact, making an alternative circuit to earth through awinding of the trunk-operators-telephone induction-coil. The tip of thetrunk-plug is thus normally disconnected from the conductor 4: andconnected to earth through the ind uctioncoil winding, so that theoperator may make the usual test by touching the tip of the plug to thethimble of the jack into which the plug is to be inserted. If there is'apotential on the jack, a click will be produced in the operatorsrelephonein the usual manner. WVhen the magnet is is excited, however,the armatures 7t" and k are drawn down, the armature 76 cuts off theground connection from the tip of the plug and closes the break in thetip-strand 4 at its front contact, and the armature it" establishesfirst the circuit 8 7 and then cuts off at spring- Zc the connection ofconductor 8 with the strand 6. The conductor 7 between the magnet g andthe armature k has a ground connection through a resistance m. Theplug-seat switch Z maintains the connection of the conductor 8 to thebattery normally open; but as soon as the plug is lifted from its socketthe battery is applied through the winding of magnet It to the conductor6, from which it finds circuit to earth through the armature g asuitable resistance.

and the sensitive magnet it. The magnet it,

as previously stated, may be of high resistbe connected by way of theregistering contacts 0 b of the plug and jack to the test-conductor 3 ofthe line and thence to earth through the cut-off relay 0, which may havea resistance of, say, thirty ohms, so that the magnet 76 will receiveincreased current and draw down its armatures k The circuit 8 7 willthus be established through the winding of magnetk and the armature kthereof to earth through the resistance m, so that the magnet 71; willremain excited until the circuit is broken by the replacement of thetrunkplug in its socket. The flow of current in the conductor 7, whichincludes the winding of magnet g, is now dependent upon the condition ofthe test-magnet /L. If the line with which connection has been made isalready engaged, there will be a potential on the testring 5 of the jackand the magnet it will re* ceive current, holding its armature up. If,however, the line to which the plngchas been connected is free, therewill be no potential on the test-ring of the jack and the magnet it willallow its armature to fallback, thus closing the circuit 7 to earth inshunt of the re sistance m. The flow of current through this shunt-pathwill excite the magnet g,

which will attract its armature g, cutting off.

the test-magnet h from connection with the sleeve of the plug andconnecting the sleeve in stead to the free pole of the battery (Zthrough Current will thus flow from the battery to conductor 6 by way ofthe armature g and its front contact, thence to the sleeve of the plugand to earth through the conductor 3, containing the cut-off relay,establishing the busy-test potential at the other multiple jacks of theline. The electromagnetic switch g, whose operation is thus dependentupon the free condition of the line to which the trunk-plug may beconnected, controls the electrical condition of the trunk-line. I haveshown two additional armatures for the magnet g, connected,respectively, with the conductors 4: 5, leading to the line-springs f fof the trunk-line jack at the answering-board. These armatures controlthe continuity of the conductors i 5 at their front contacts, so that inthe normal condition of the switch the circuit of the trunk-line isbroken. The armature of magnet g, which is connected to the strand 5 ofthe trunk-circuit, normally rests against a back contact-anvil, which isconnected to earth by a conductor 9. Said conductor 9 includes thesecondary winding of an induction-coil whose primary winding is includedin a local circuit with a constantlyrunning interrupter a to produce acharacteristic tone-test on the trunk-line. \V hen the magnet g isexcited, the circuit of the trunkline is completed and the ground-00nductor 9 is disconnected, while at the same time, as before explained,the test-magnet 72/ is disconnected from the sleeve of the plug and abattery connection substituted therefor.

At the answering-switchboard 1 have shown a pair of plugs and aplug-circuit oi a wellknown type for uniting lines. The plugs of thispair each have the usual three contacts, the tip and ring contacts ofeach plug being inductively connected with the corresponding contacts ofits mate through the windings of a repeating-coil and the sleeve of eachplug being connected to the free pole of a grounded battery. Thisbattery is connected in a bridge of the plug-circuit conductors, whichlead to the tip and ring contacts of the left-hand plug, which isdesigned for insertion in the jackf of the trunk-line, and the usualsupervisory relay 0 is included in the circuit between the free pole ofthe battery and the ring-contact of the plug. This supervisory relay 0controls a normally open shunt about the supervisory signal-lamp 0,which is included in the conductor 10, leading from the free pole of theplug-circuit battery to the left-hand plug. The third contact or thimblef of the springjael; fot' the trunk-line forms the terminal of aconductor 11, which leads with the other trunkline conductors to the Bswitchboard, being led to earth at the last mentioned board through thewindings of a relay-magnet 7 When the plug is inserted in thespring-jack f at the answeririg-switchboard A, therefore,

the circuit 10 11, including the supervisory lamp 0 at theanswering-board and the magnet 2) at the trunking-board, is completed.The magnet 39 is excited by current flowing in this circuit and thesupervisory lamp 0 is brought under the control of the supervisory relay0. The magnet 79 has an armature 1), which is connected, through asignal-lamp g, with the lover or moving part of the plugseat switch. Thenormal resting contact of the armature-lever p is connected to earththrough a resistance, and the front contact of said armature-lever isconnected to the battery (Z. The plug-seat switch has alternativecontacts, the switch-lever thereof beingconnected to the Winding ofmagnet Z; and normally resting against a contact which is connected tothe free pole of the battery (Z, while the alternate contact of saidswitch Z, closed while the plug is in the seat, is connected to earththrough the resistance r.

The usual order-wire is shown extending from the operators telephone 6at the trunking-switchboard B to a special order-wire listoning-key s atthe answcling-switchboard A,

said listening-key 8 being adapted when depressed to connect the Aoperators telephone 25 with the order-wire. The A operator also has theusual listening-key for connecting her telephone set in a bridge of thatside of her plug-circuit which is intended for connection with thetrunk-line.

It will be understood, of course, that the A operator would be providedwith the ordinary ringing-keys and sources of current controlled therebyfor operating the bells at stations A B.

The operation of the system may be traced as follows: Assuming that theA operator has a call say from the subscriber at station A- for asubscriber whose line terminates at switchboard B-say subscriber atstation B she makes connection with the calling-line by means of heranswering-plug, inquires the number of the called subscriber, andfinding it to be a call which will necessitate the use of a trunk-lineto the board B she depresses her order-wire key 8, gives the number ofthe subscriber wanted, and receives in return information as to whichtrunk-line to use. The A operator then inserts her connectingplug (theone on the left hand) into the springjack f of the trunk-line which theBoperator has designated. The line conductors of the calling-line arethus extended to the conductors 4c 5 of the trunk-line, and so to the Bswitchboard, and the signaling-circuit 1O 11 is also completed, wherebythe magnet 19 at the board B is excited. If the B operator has not yetpicked up the terminal pluge of the trunk which she has designated, thelever of the plug-seat switch Zwill be forced over against itsground-contact, and the armature 19 being drawn up by the magnet 19 acircuit will be completed from the battery (Z through the resistance 7'to earth, thus lighting the signallamp 9 and indicating that thetrunk-line has been plugged into at theAboard. The operator B thereuponpicks up the trunk-plug e and inserts it in the jack of the calledsubscriber. The lamp q is then short-circuited by the plugseat switchand extinguished.

I prefer to leave the B operator the usual apparatus for making apreliminary busy-test. This will be desirable where the called party hasa number of lines running into the switchboard B, as is frequently thecase where a.

subscriber has much telephone business. The B operator may thus test theseveral lines of the called party until she finds one that is not busyand inserts the plug into the jack of that line; but if on testing shefinds that all the lines of the called party are busy she inserts theplug 6 into the spring-jack of any one of said lines regardless of itsbusy condition. As soon as the plug 6 is lifted from its seat thecircuit 8 6 is established, as previously explained, exciting thetest-magnet it, so that the latter draws up its armature and breaks thenormal ground connection through the magnet g. Then when the plug isinserted in the spring-jack the magnet k responds, as'previouslyexplained, and draws up its armatures, cutting off the ground connectionthrough the operators induction-coil from the tip of the plug and alsocutting off the battery connection 8 from the conductor 6, thus leavingthe test-magnet h in said conductor connected only with the sleeve ofthe plug, so that the excitement of said magnet will depend upon theexistence of a test-potential at the thimble of the jack into which theplug has been inserted. At the same time the local circuit 8 7containing the winding of magnet g is established, said circuit beingcontrolled at the armature and back contact of the test-magnet h. Inother words, by the insertion of the plug 6 into the spring-jack of thecalled line the electromagnetic switch g is brought under the control ofthe test-magnet it. Now if the line called for is free there will be nopotential on the test-ring of the jack, and the magnet h which washeretofore excited by current in the circuit 8 6 will be deprived ofcurrent and allow its armature to fall back, closing the local circuit,including the electromagnetic switch 9, whereupon said switch will beactuated, completing the circuit of conductors L and 5 of thetrunk-line, disconnecting the test-magnet h from the sleeve of thetrunkplug, and substituting a battery connection therefor; but if aconnection already exists withv the called line at some other multiplespring-jack thereof the magnet h, which is sensitive to thetest-potential at the springjack, will keep its armature drawn up andthe local circuit containing the switch y consequently open. The switchQ will therefore remain inert,leaving the circuit of the trunklinebroken and the ground conductor 9 containing the secondary Winding ofthe signaling induction-coil connected to the trunk-conductor 5. Theoperator at board A will therefore hear in her telephone acharacteristic hum or tone, which will inform her that the desiredconnection has been made, but that the line called for is for the timebeing busy. Circuit will also be completed from the A operatorsplug-circuit battery through the supervisory relay 0 to the conductor 5of the trunk-line and thence through conductor 9 to earth, so that aslong as the called partys line is busy the supervisory lamp 0 will beshunted out. As soon, however, as the called line has been freed fromits previous connection at some other spring-jack the magnet it will bedeprived of current and will allow its armature to fall back, closingthe local circuit of the electromagnetic switch g and bringing about theestablishment of a complete operative connection between the trunklineand the line in whose spring-jack the trunk-plug has been inserted. Theconductor 9 is also disconnected from the trunk-line, so that thebattery-circuit from conductor 5 to said lamp to light.

earth will be broken and the supervisory relay 0 will allow its armatureto fall back, breaking the shunt about the lamp 0' and causing Uponseeing this signal the A operator knows that a complete operativeconnection with the called line has been established. The calledsubscriber may now be signaled in the usual way, which need not here bedescribed, and the connection may be supervised from the A board inaccordance with the well-known practice. When the subscribers havefinished conversation and the A operator, who has supervised theconnection, pulls out the plugs, the circuit 10 11 is broken and magnet19 at the board B allows its armature to be retracted. A circuit frombattery d through the lamp 9 is thus completed by way of the plug-seatswitch, the armature p and its back contact, and the resistance 1', andthe lighting of this lamp may be takenas a signal to the B operator totake down the connection. When the plug is replaced in its socket, theplug-seat switch Z is operated, breaking the circuits through the lamp qand the magnets 7 and 5 so that the apparatus is restored to itsoriginal condition in readiness for another connection.

It will be observed that the connection of the trunk-plug with a busyline does not in any way interfere with the signaling on such line, nordoes it impair the transmission, since the connection of thehigh-resistance magnet h to the test-conductor 3 of the line is notsufficient to change materially the flow of current through theconductor which includes the cut-off relay.

Having thus described my invention, Iclaim as new, and desire to secureby Letters Patent, the following:

1. The combination with a telephone-line having multiple spring-jacks,of a circuit terminating in a switch-plug adapted for insertion in aspring-jack to make connection with the line, a test-conductor extendingto all the multiple spring-jacks, means for making connection with theline at any of the multiple spring-jacks thereof, and means for changingthe electrical condition of the test-conductor in making connection atany spring-jack, an electromagnet included in a conductor whichterminates in a contact-piece of the aforesaid plug and brought therebyinto circuit with the test-conductor of the line when the plug isinserted in a spring-jack thereof, a switch adapted when actuated todisconnect the magnet from the test-conductor and to operate othermechanism, and means controlled by the cooperation of the plug and thespring-jack into which it may be inserted, for bringing the switch underthe control of said magnet, whereby when the plug is inserted in thespringjack, the condition of the switch and its con trolled mechanism isdependent upon the busy or free condition of the line.

2. The combination with a telephone-line having multiple spring-jacks,of means for making connection with the line at any of the spring-jacks,means controlled by connection at one of the spring-jacks forestablishing a peculiar electrical condition at the other spring-jacks,a circuit terminating in a switchplug adapted for insertion in aspring-jack of the line to make connection therewith, a testmagnet andswitching mechanism adapted to be controlled thereby, for changing theelectrical condition of the circuit having the plugterminal, said magnetbeing associated with the plug and sensitive to the electrical conditionof the spring-jack into which the plug may be inserted, and meansactuated by the insertion of the plug into a spring-jack for bringingsaid switching mechanism under the exclusive control of the test-magnet,whereby the electrical condition of the circuit having the plug-terminalis dependent upon the busy or free condition of the line with which theplug may be connected.

3. The combination with a circuit terminating in a switch-plug at aswitchboard having spring-jacks into which the plug is adapted to beinserted, of a conductor terminating in a contact-piece of the plug, twobranches from said conductor, one containing an electrical responsivedevice sensitive to an electrical potential which may be applied to thespringjack in which the plug is inserted, the other branch beingconnected to a source of current, a switch normally closing thefirst-mentioned branch and adapted alternatively to open the firstbranch and close the second, mechanism actuated in the operation of saidswitch for changing the electrical condition of the circuit having theplug-terminal, means for operating said switch, adapted to be controlledby the magnet, and means actuated in the insertion of the plug, forbringing the switch under the control of the magnet, whereby upon theinsertion of the plugin a spring-jack, the electrical condition of theplug-circuit will be made dependent upon the potential at the jack withwhich connection is made, as set forth.

4:. The combination with a telephone-line having multiple spring-jacks,of a circuit terminating in a switch-plug adapted for insertion in aswing-jack of said line to make connection therewith, means for makingconnection with the line at the other spring-jacks, means forestablishing a test-potential at all the spring-jacks of the line duringthe existence of a connection at one of such other spring-jacks, atesting device associated with the aforesaid plug sensitive to thetest-potential of the jack into which said plug may be inserted,switching mechanism brought into action upon the response of saidtesting device to the failure of the test-potential at the jack in whichthe plug is inserted, controlling the circuit which has theplug-terminal, and adapted further to render said testing deviceindependent of the electrical condition of the jack,

as by disconnecting the said device therefrom, and means actuated uponthe operation of the last-mentioned switching mechanism, forreestablishing the test-potential at the springjacks of the line.

5. The combination with a telephone-circuit, of a magnet 7L andswitching mechanism controlled thereby for changing the electricalcondition of said telephone-circuit, a local circuit containing saidmagnet in a branch thereof, means for producing a flow of current insaid local circuit, and switching mechanism brought into action throughthe agency of said magnet when the same becomes inert, for rendering themagnet irresponsive to the flow of current in said local circuit, as bydisconnecting the branch containing the magnet, substantially as setforth.

6. The combination with a telephone-circuit, of a plug and spring-jackswitch therefor, a local test-circuit established in contacts of saidswitch, means for changing the electrical condition of saidtest-circuit, a relaymagnet It in a normally closed branch of thetest-circuit, an electromagnetic switch adapted when excited to closethe telephone-circuit and simultaneously to render the relay-magnet 7Lindependent of said test-circuit, as by disconnecting the sametherefrom, and means controlled by the insertion of the plug in thespring-jack, for establishing a local circuit for said electromagneticswitch, controlled at resting-contacts of said relay, whereby thecondition of the telephone-circuit is made dependent upon the conditionof the test-circuit when the plug is inserted in the spring-jack.

7 The combination with a telephone-line having multiple spring-jacks, ofa telephonecircuit terminating in a switch-plu g adapted to be insertedin a spring-jack of the telephoneline to make connection therewith,means for making connection at the other spring-jacks, and meansactuated in making connection with the line for changing the electricalcondition of the spring-jacks thereof, a testing device associated .withthe plug and sensitive to the electrical condition of the spring-jackinto which said plug may be inserted, switching mechanism actuated inthe response of said testing device, for rendering said device independent of the electrical condition of the spring-jack into which theplug is inserted, and a signal-circuit also controlled through theagency of said testing device.

8. The combination with a telephone-line having multiple spring-jacks,of a circuit terminating in a switch-plug adapted for insertion in aspring-jack to make connection with said line, a test-conductorextending to all the multiple spring-jacks, means for making connectionwith the line at any of the multiple spring-jacks thereof, and means forchanging the electrical condition of the test-conductor in makingconnection at any spring-jack, a conductor terminating in acontact-piece of the plug and adapted to form a local circuit with saidtest-conductor when the plug is inserted in a spring-jack, anelectromagnet included in a normally closed branch of said local circuitand sensitive to the electrical condition of the test-conductor, andswitching mechanism controlled by said magnet adapted when actuated tochange the electrical condition of the telephone-circuit andsimultaneously to render said magnet independent of the local circuit,as by disconnecting the same therefrom, substantially as set forth.

9. The combination with a telephone-circuit, of a local circuit andmeans for producing a current therein, a relay in a branch of said localcircuit, and switching mechanism actuated through the agency of saidrelay when the same becomes inert, adapted to change the electricalcondition of the telephone-circuit and also to render said relaythereafter independent of the flow of current in said local circuit, asby disconnecting the said branch containing the relay.

10. The combination with a-telephone-circuit and a plug and spring-jackswitch controlling the same, of a local circuit established in contactsof said switch, and means for producing a flow of current therein, arelay-magnet ]L in a branch of said local circuit, a switchcontactactuated through the agency of said relay-magnet when the same becomesinert, adapted to change the electrical condition of saidtelephone-circuit, and another switch-contact simultaneously actuated,for disconnecting the branch containing the relay-magnet.

11. he combination with aplug and springjack switch and atelephone-circuit controlled thereby, of a local circuit established incontacts of said switch, means for producing a flow of current in saidcircuit, a conductor terminating in a contact-piece of the plug andforming a part of said local circuit, a relaymagnet responsive to theflow of current in said conductor, switching mechanism adapted to closea normally open break in the telephone-circuit and to cut oif therelay-magnet from the path of current in said local circuit, and meansactuated in the insertion of the plug for bringing said switchingmechanism under the control of the said relay-magnet, said mechanismbeing actuated by the relay when inert, whereby the condition of thetelephone-circuit is made dependent upon the condition of the localcircuit.

12. The combination with a plug and springjack switch and atelephone-circuit controlled thereby, of a local circuit established incontacts of said switch, means for producing a flow of current in saidlocal circuit, a magnet in a conductor terminating in the plug andforming a part of said local circuit, switching mechanism controllingthe telephone-circuit, and means actuated in the insertion of the plugin the spring-jack for bringing said switching mechanism under thecontrol of said magnet,

whereby the condition of the telephone-circuit is made dependent uponthe condition of the local circuit.

13. The combination with a telephone-line and multiple spring-jacksthereof having test contact-pieces, of a telephone-circuit terminatingin a switch-plug adapted to be inserted in a spring-jack ofthetelephone-line to make connection therewith, means for making connectionat the other'spring-jacks, and means actuated in making connection withthe line for establishing a test-potential at the test contact-pieces ofthe several multiple springacks thereof, a relay 71 in a conductorterminating in a contact-piece of the plug which is adapted to engagethe test-contact of the spring-jack into which said plug may beinserted, said conductor forming a branch of a local circuit for therelay, said. relay being thus responsive to the test-potential at thejack, an electromagnetic switch in a local circuit closed by saidrelay/z when the same is inert, said electromagnetic switch controllingthe circuit which has the plug-terminal, a source of current connectedwith said relay ii to maintain the same excited independent of thecircuit thereof closed at the test-contact of the jack, and meansactuated in the insertion of the plug in the spring-jack, fordisconnecting said source of current from the relay, whereby thecondition of the circuit having the plug-terminal is made dependent uponthe busy or idle condition of the line into whose spring-jack the plugis inserted.

14. The combination with a trunk-line extending between twoswitchboards, of a signal 0 and a testing appliance t associated withthe trunk-line at one of the switchboards, a telephoneline, and aconnectionswitch for establishing connection between the trunk-line andthe telephone-line at the other switchboard, a source of busy-test po-'tential, and a switch for applying said potential to the telephone-line,and an electromagnetic switch it controlling the circuit of thetrunk-line, said electromagnetic switch being sensitive to the presenceof busy-test potential on the said telephone-line, whereby the busy orfree condition of the line is automatically indicated.

15. The combination with a telephone-line having a busy-test conductor3, a source of test-potential and a switch for applying the same to saidtest-conductor, a second telephone-circuit 4 5, and a connection-switcha for uniting the two telephone-circuits, a testmagnet lb and a switch ghaving normally closed contacts connecting said test-magnet to thetest-conductor, a signal 0 associated with the second telephone-circuit,controlled through the agency of said switch g, and means made operativeby the test-magnet when it becomes inert, for actuating said switch 9,whereby the circuit of the test-magnet is broken and the signal I)actuated upon a failure of the test-potential applied to saidtest-conductor.

16. The combination with a telephone-line having multiple terminals, ofa connectionswitch adapted to be applied to one of said terminals, asource of test potential applied by said switch to all the said multipleterminals, a second connection-switch adapted to engage another of saidmultiple terminals, a magnet associated with said secondconnection-switch responsive to the failure of the test-potential at themultiple terminal with which said last-mentioned connection-switch isengaged, and a switch 9 controlled by said magnet adapted to disconnectthe magnet and reestablish a test-potential at the several multipleterminals.

17. The combination with a telephone-line and multiple spring-jackstherefor, of a plug and plug-circuit, a trunk-circuit also having aplug-terminal, a local busy-test circuit composed of three conductors,one extending to a contact-piece on each of the multiple spring jacks,another associated with the trunk-plug and including a test-magnet, andthe third associated with the other plug, a battery included in saidtest-circuit to actuate the test-magnet when the test-circuit iscompleted by the insertion of the trunk-plug and the other plug intomultiple spring-jacks respectively of the same line, a signal device atthe distant end of the trunk-line, and means for actuating said signaldevice controlled by said test-magnet.

In witness whereof I hereunto subscribe my name this 18th day of April,A. D. 1902.

ED'WIN H. SMYTHE.

"Witnesses: 7

JOHN G. RoBnR'rs, FREDERICK A \NATKINs.

